// #pragma GCC optimize("Ofast,no-stack-protector,unroll-loops",                  \
//                      "omit-frame-pointer", "inline")
// #pragma GCC target(                                                            \
//     "sse,sse2,sse3,ssse3,sse4,sse4.1,sse4.2,popcnt,abm,mmx,avx,avx2,fma,tune=native")
// #pragma GCC option("arch=native", "no-zero-upper") // Enable AVX

/// UH Top
#include <bits/stdc++.h>
#define db(x)   cerr << #x << ':' << (x) << '\n';
#define all(v)  (v).begin(), (v).end()
#define allr(v) (v).rbegin(), (v).rend()
// #define int ll
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
// typedef __int128_t int128;
typedef pair<ll, ll> pii;
typedef pair<ld, ll> pdi;
typedef pair<ld, ld> pdd;
typedef pair<ld, pdd> pdp;
typedef pair<string, ll> psi;
typedef pair<ll, string> pls;
typedef pair<string, string> pss;
typedef pair<ll, pii> pip;
typedef pair<pii, pii> ppp;
typedef complex<ld> point;
typedef vector<point> polygon;
typedef vector<ll> vi;
typedef pair<point, int> ppi;
#define prec(n)                                                                \
	cout.precision(n);                                                         \
	cout << fixed
const ll mod = (1e9 + 7);
const ld eps = (1e-9);
const ll oo = (ll)(1e9 + 5);
#define pi   acos(-1)
#define MAXN (ll)(1e6 + 5)

int32_t main() {
	ios_base::sync_with_stdio(0);
	cin.tie(0);

	int n;
	cin >> n;
	string s;
	cin >> s;
	vector<int> adds = {0, 1, 2, 2, 1, 0};
	string x = "spbsu$";
	vector<vector<int>> dp(n + 1, vector<int>(6, oo));
	dp[0][0] = 0;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < 6; j++)
			dp[i + 1][j] = min(dp[i + 1][j], dp[i][j] + adds[j]);
		for (int j = 0; j < 5; j++)
			if (s[i] == x[j])
				dp[i + 1][j + 1] = min(dp[i + 1][j + 1], dp[i][j]);
	}

	cout << dp[n][5] << "\n";

	return 0;
}